Manufacture of high accuracy through bore synchro



Nov. 10, 1964 s. M. ORIGONI ETAL MANUFACTURE OF HIGH ACCURACY THROUGH BORE svucuao Filed April 26, 1960 2 Sheets-Sheet 1 C'I-MPLES W LANG INVENTOR5 ATTORN EYS 1964 s. M. ORlGONl ETAL MANUFACTURE OF HIGH ACCURACY THROUGH BORE SYNCHRO Filed April 26, 1960 2 Sheets-Sheet 2 him I INN 5/1 we M 0260M 644-2455 W AAA/6 1 EN TOR {fan-W ATTORNEYS United States Patent 3,156,076 MANUFACTURE OF HIGH ACCURACY THRQUGH BORE SYNCHRG Silvie Michael Origoni, River Vale, and Charles W. Lang, Pompton Plains, N..I., assignors to General Precision, Inc., Little Falls, N.J., a corporation of Delaware Filed Apr. 26, 1960, Ser. No. 24,793 Claims. (Cl. 51-281) This invention relates generally to improvements in dynamoelectric synchros and more particularly to improvements in the process of making such synchros, and in the construction of the synchro to improve the accuracy of such devices to within one minute of are or better.

It is, accordingly, a principal object of the invention to provide an alternating current synchro of greater accuracy than the conventional type of synchro.

A further object is to provide a synchro construction having a uniform air gap between the rotor and stator members during relative rotation therebetween and a minimum of eccentricity and angular variation between the stator and rotor.

A still further object is to provide an improved method of manufacturing such a synchro.

Other objects and many additional advantages will be more readily understood by those skilled in the art after a consideration of the following specification taken with the accompanying drawings, wherein:

FIGURE 1 is a longitudinal sectional view illustrating details of one preferred synchro construction according to the invention;

FIGURE 2 is a longitudinal sectional view of one preferred rotor construction;

FIGURE 3 is an enlarged section taken along lines 33 of FIGURE 2, illustrating the rotor slot construction;

FIGURE 4 is a schematic diagram of the coil arrangement for assistance in understanding the preferred coil winding arrangement in the rotor;

FIGURE 5 is a longitudinal sectional view similar to FIGURE 2 illustrating one preferred stator constaruction;

FIGURE 6 is an enlarged section taken along lines 6--6 of FIGURE 5, illustrating the stator slot construction, and

FIGURES 7 and 8 are elevational views of portions of the stator and rotor laminations, respectively.

Referring now to FIGURE 1 for a detailed consideration of a preferred embodiment of the invention and its manner of construction, there is shown a synchro comprising an outerhousing 10 supporting a stator assembly, including a stator core 11 provided with stator windings, generally indicated as 12, and being disposed peripherally about the inside of the housing 19.

Within the housing and surrounded by the stator and the windings 12 thereof, is positioned a cylindrical rotor assembly 14 including a core 14 having windings 15 about the outer circumference thereof that are uniformly spaced from the stator windings by an air gap 16. Rotor assembly 14 also includes a central shaft 13 having a pair of hub portion extensions 22 at opposite ends thereof, that in turn are rotatively supported by ball-bearings l7 and 18 or other type of anti-friction bearings, thus enabling the rotor member 14 to be rotated as a unit within the housing and stator.

For energizing the rotor windings 15, individual leads 19 (one shown in FIG. 1), taken from the various windings 15, are connected with individual commutator rings 20 supported in a spaced arrangement on a molded or otherwise formed non-conducting commutator cylinder 21 that in turn is supported on and rotatable with the rotor assembly 14. Fine wire brushes 23, connected with terminals 33 supported by a stationary end wall 24 of the housing, engage the commutator rings 20 while they are rotated to transmit electrical currents to and from the rotor windings 15, as desired. Since the stator windings are fixed and stationary in the housing 10, they are energized through fixed leads 25 and stationary terminals (not shown).

According to the present invention, there are provided a number of novel construction features that considerably increases the accuracy and precision of the synchro, reducing the error to not greater than one minute of arc. Among others, there is provided a construction that maintains substantially uniform the width of annular air gap 16 between the rotor and stator for all rotative positions of the rotor member. This is accomplished by reducing to a minimum, consistent with manufacturing accuracy, the eccentricity of the rotor with respect to the stator by so constructing and intcrfitting the various surfaces of both members that they are originally made coaxial with one another with a high degree of precision and interfitted in the same manner. Other features include improvements in the construction and arrangement of the slots and windings in the rotor and stator members for the purpose of achieving a sinusoidal distribution of the magnetic flux, thereby minimizing the amplitude of undesirable slot harmonics, and raising the frequency of the fundamental slot harmonic, all to the end of further reducing the error in the synchro.

Referring to FIGURE 1 for an understanding of the novel mode of fabrication which minimizes the eccentricity of the rotor relative to the stator, the stator and housing are initially machined by means of a through bore type technique. More specifically, the stator 11 and windings 12 are initially inserted and suitably fastened in place within the housing 10. Thereafter, the inner peripheral surface of the stator surrounding the air gap 16 and the housing bearing bore surfaces 26 and 27, are all simultaneously ground in one operation to roundnesses and taper tolerances in the order of 30 millionths of an inch or better. This simultaneous internal grinding or honing of the stator surface and housing bearing journals insures that all of these surfaces are made precisely coaxial with one another to a degree not obtainable if these surfaces were separately machined.

In a second operation, the rotor assembly 14 is made and assembled with the windings 15 provided thereon. Thereafter in a single operation the. outside peripheral surface of the rotor core 14 is ground and polished on ball centers to a roundness of at least 20 millionths of an inch or better While at the same setting and with the same precision, the rotor shaft extension 22 are ground and polished at the locations 28 and 29 to provide the inner race journals for the balls of the ball-bearings 17 and 18. This simultaneous grinding and polishing of the ball bearing inner race angular contact journals 28 and 29 with the outside surface of the rotor core 14' insures that all of these surfaces are made precisely coaxial with one another about the synchro central axis to a degree not obtainable if these surfaces were separately machined. Additionally, it is noted that the inner race journals 28 and 29 for the balls of the ball-bearings are formed directly on the rotor shaft extensions 22 and hence made precisely coaxial with the outside periphery of the rotor.

After the stator and rotor structures have been machined in this manner, the cylindrical members 30 and 31 forming the outer races for the bearings are line lap fitted to the housing bearing journal surfaces 26 and 27, by line lapping the surfaces 26 and 27 to accept the bearing outer race members 3% and 31. The outer bearing race members 36 and 31 are, of course, previously precision ground and polished, whereby this manner of assembly thereof to the housing journals 26 and 27 permits but a minimum degree of eccentricity.

In the remaining series of operations, the end plates 32 and 24, brushes Z3, electrical connections and the like are made, assembled and connected by bolts or other suitable fasteners, as shown, and the outer right-hand cover plate 34 is finally added to complete the improved synchro construction.

It is to be particularly emphasized that the inside peripheral surface of the stator ll is made precisely coaxial withthe housing assembly bearing journal surfaces 26 and 27, which in turn are made precisely coaxial with the surfaces 23 and 29 on the rotor shaft extensions 22 that form the inner race journals for the balls of the ballbearings 1'7 and 18. Consequently, the inner surface of the stator defining one circumferential surface of the air gap in is precisely coaxial with the inner race journals 23 and 29 on the rotor shaft. Moreover, the inner race journals 2%; and 25 are also made precisely coaxial with the outer peripheral surface of the rotor core 114 defining the second circumferential surface of air gap 16, whereby it is believed evident that the confronting circumferential stator and rotor surfaces defining the air gap 16 are also precisely coaxial with one another to provide a constant air gap width betweenthese members for all relative rotative positions therebetween.

As generally indicated above, there is also provided, according to the present invention, improvements in the construction of the stator and rotor laminations and in the manner of inserting the windings and their order of in sertion to provide a sinusoidal distribution of the magnetic flux with a minimized amplitude of the fundamental slot harmonic. There is also provided an improved arrangement of the number of slots and windings on the stator and rotor to raise the frequency of the fundamental slot harmonic, as is desired.

For example, according to one preferred embodiment of the invention, the stator is provided with thirty-six evenly distributed slots and a total of nine windings thereon in overlapping relationship, and the rotor is provided with twenty-eight slots and a total of seven evenly distributed windings thereon. Each winding on both the stator and rotor is provided with four equally spaced coils, one in each quadrant, with each coil occupying two slots. Consequently, with this arrangement, each slot symmetrically contains, in complete overlapping relationship, the wires of two coils to reduce the error, and the lowest order harmonic being generated is the two hundred and fifty second (252ml).

Referring to FIGURES 2 to 8, for a more complete understanding of the construction of the stator and rotor assemblies, FIGURE 8 illustrates a sector of one of the rotor laminations 49 having the slots 41 formed about the periphery thereof. A series of such laminations 40 are stacked together, with the slots 41' in aligned array, to form the body portion of the rotor assembly 14 as shown in FIGURE 2, and the turns of the winding coils R are inserted into the channels formed by the aligned slots, as illustrated in'FlGURE 3.

To obtain the desired sinusoidal distribution of the magnetic flux, the turns are distributed about the rotor in direct proportion to the sine of their respective pitch angles, as illustrated in the diagrammatic view of FIG- URE 4. Referring to FIGURE 4, there is schematically represented an end view of the rotor assembly l4 having a central axis 43 passing therethrough. The pitch angle at of the windings is the angle formed between vertical line 45 and a radial line 44 extending from the central axis 43 to the periphery of the rotor assembly 14. As shown, therefore, the turns .of the windings are distributed in direct proportion to the sine of the pitch angle a;

FIGURES. 5, 6 and 8 illustrate similar details of the stator construction showing in FIGURE 7 a stator lamination as having inwardly opening slots 47 therein dis- 4 tributed uniformly about its inner periphery. A plurality of stator laminations such as 46 are stacked together with their slots in alignment, as shown in FIGURE 5, and the turns of the stator coils 12 are inserted in the slotted openings best shown in FIGURE 6.

To further reduce the amplitude of the undesired fundamental slot harmonic, the turns of the stator and rotor windings are also skewed along the length of these members.

What is claimed is:

l. A method of fabricating a high-precision dynamoelectric device in which a cylindrical rotor member having a coaxial shaft extension at each end is mounted for coaxial rotation in a hollow cylindrical housing and stator assembly by means of respective ball bearing sets journaling the shaft extensions in the housing, said method comprising:

precision grinding the stator assembly to produce a cylindrical inner surface thereon while simultaneously grinding journals in the housing for the outer races of the ball bearing sets, said journals consisting of respective cylindrical surfaces coaxially disposed adjacent each end of the housing and stator assembly;

precision grinding the rotor member to produce, in a single setting and operation, a cylindrical outer surface thereon complementary to said stator assembly cylindrical inner surface and, on each of the shaft extensions, respective ground and polished, coaxial, inner ball-races for the ball bearing sets, located complementary to the outer race journals ground on the housing and stator assembly; and

line lap fitting a ball bearing outer race member into each of said outer racejournals. 2. A method of fabricating a high-precision dynamoelectric device in which a cylindrical rotor member having a coaxial shaft extension at each end is mounted for coaxial rotation in a hollow cylindrical housing and stator assembly by means of respective ball bearing sets journaling the shaft extensions in the housing, said method comprising:

precision grinding the stator and housing assembly to produce simultaneously a pair of coaxially-spaced cylindrical inner surfaces of equal diameter on said. housing each adjacent a respective end thereof and, intermediate said surfaces, 21 third coaxially-aligned cylindrical inner surface of equal diameter on the stator, each of said pair of surfaces constituting a journal for the outer race member of a ball bearing set;

precision grinding the rotor member to produce, in a single setting and operation, a cylindricalouter surface thereon complementary to said stator assembly cylindrical inner surface and, on each of' the shaft extensions, respective ground and polished, coaxial, inner ball-races for the bail bearing'sets, located complementary to the outer race journals ground on the housing and stator assembly; and

line lap fitting a ball bearing outer race each of said outer race journals.

3. A method according to claim 2 wherein the inner cylindrical surface of the stator and said outer race jourrials are line ground to a tolerance in the order of '30 millionths of an inch; and a the outer cylindrical surface of the rotor and said inner ball races are ground and polished to a tolerance in the order of 20 millionths of an inch.

4. A method of fabricating a high-precision dynamoelectric device in which a cylindrical rotor member having a coaxial shaft extension at each end is mounted for coaxial rotation in a hollow cylindrical housing and stator assembly by means of respectiveball bearing sets journaling the shaft extensions in the'housing, said method comprising: r a

providing a hollow cylindrical housing member having coaxially mounted therein a stator assembly'includmember into ing a laminated core of hollow cylindrical configuration;

precision grinding the inner surface of said core to a predetermined diameter while simultaneously grinding respective bearing journals adjacent the ends of said housing to the same diameter as, and exact concentricity With, said inner surface;

providing a rotor member including a cylindrical laminated core and a coaxial cyl-indrical extension of smaller diameter at each end;

precision grinding the circumferential surface of said rotor core to a predetermined diameter and with the same setting of the grinding apparatus and in the same operation grinding and polishing respective coaxial ball bearing inner race surfaces on said cylindrical extensions; and

line lap fitting a ball bearing outer race member in each of said bearing journals.

5. A method of fabricating a high-precision dynamoelectric device in which a cylindrical rotor member having a coaxial shaft extension at each end is mounted for coaxial rotation in a hollow cylindrical housing and stator assembly by means of respective ball bearing sets journaling the shaft extensions in the housing, said method comprising:

and

line lap fitting the outer ball-bearing race to the housing outer race bearing journals.

References Cited by the Examiner UNITED STATES PATENTS Brady 310-258 Flatiand 310-180 Bryant et al 308-178 Hanna 310-180 Wieseman 310-90 Glass 310-258 Brown 310-42 Jones et a1 308-178 MILTON O. HIRSHPTELD, Primary Examiner. ORIS L. RADER, Examiner. 

1. A METHOD OF FABRICATING A HIGH-PRECISION DYNAMOELECTRIC DEVICE IN WHICH A CYLINDRICAL ROTOR MEMBER HAVING A COXIAL SHAFT EXTENSION AT EACH END IS MOUNTED FOR COAXIAL ROTATION IN A HOLLOW CYLINDRICAL HOUSING AND STATOR ASSEMBLY BY MEANS OF RESPECTIVE BALL BEARING SETS JOURNALING THE SHAFT EXTENSIONS IN THE HOUSING, SAID METHOD COMPRISING: PRECISION GRINDING THE STATOR ASSEMBLY TO PRODUCE A CYLINDRICAL INNER SURFACE THEREON WHILE SIMULTANEOUSLY GRINDING JOURNALS IN THE HOUSING FOR THE OUTER RACES OF THE BALL BEARING SETS, SAID JOURNALS CONSISTING OF RESPECTIVE CYLINDRICAL SURFACES COAXIALLY DISPOSED ADJACENT EACH END OF THE HOUSING AND STATOR ASSEMBLY; PRECISION GRINDING THE ROTOR MEMBER TO PRODUCE, IN A SINGLE SETTING AND OPERATION, A CYLINDRICAL OUTER SURFACE THEREON COMPLEMENTARY TO SAID STATOR ASSEMBLY CYLINDRICAL INNER SURFACE AND, ON EACH OF THE SHAFT EXTENSIONS, RESPECTIVE GROUND AND POLISHED, COAXIAL, INNER BALL-RACES FOR THE BALL BEARING SETS, LOCATED COMPLEMENTARY TO THE OUTER RACE JOURNALS GROUND ON THE HOUSING AND STATOR ASSEMBLY; AND LINE LAP FITTING A BALL BEARING OUTER RACE MEMBER INTO EACH OF SAID OUTER RACE JOURNALS. 